Electrical resistance welding (e.g. spot welding, projection welding, etc.) is known, and involves squeezing/pinching the components of a work-piece to be welded between a pair of opposed electrodes, and passing sufficient electrical current through the electrodes and components to melt and fuse the components together.
It is also known to sequentially pass a series of work-pieces to be welded through a welding station, and to use a robot to move the welding electrodes into place in the welding station to make the weld. Thereafter, the robot moves the electrodes out of the way as another work-piece moves into the welding station. It is also known to periodically move the electrodes into an electrode dressing station to machine or otherwise shape the electrode tips to a prescribed configuration.
It is essential for weld quality that the welding electrodes be aligned with each other, and with the work-piece, within suitable tolerances. Unfortunately, such tolerances are sometimes exceeded in the course of welding numerous work-pieces one after the other, or between production runs, incident to the welding equipment being damaged through rough handling, violent contact with fixtures, or incorrect presentation to the work-piece which can result in the electrodes being forced out of alignment with each other and with the work-piece.
Heretofore, alignment of the welding electrodes has been determined either by occasional visual inspection of the electrodes by equipment operators or maintenance persons, or by the observance of poor welds on the work-piece downstream of the welding station. The present invention provides a method and apparatus for the automatic mechanized inspection of electrode alignment, and signaling of the welding operator when untoward misalignment exceeds a prescribed amount.